Precast Concrete Segmental Bridges America's Beautiful and Affordable
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HISTORICAL-TECHNICAL SERIES Precast Concrete Segmental Bridges America’s Beautiful and Affordable Icons How did precast concrete segmental construction become a major player in the modern American bridge industry? While the continuing growth in market share for precast, prestressed concrete systems can be attributed to numerous competitive advantages, this article presents an overview of the proliferation of segmental bridges in the United States based primarily on five advantages — economy, construction efficiency, durability, design innovation and aesthetics. Linda Figg President and Director of Bridge Art a bridge type that would be many other countries throughout the FIGG Engineering Group come an increasingly popular world. Typically, the precast, pre Tallahassee, Florida Forand successful competitor over stressed concrete bridge also proves to alternative building systems, precast be the most cost-effective alternative concrete made a rather unpretentious for owners, particularly when life- debut in the United States. Indeed, one cycle costs such as maintenance and wonders if the engineers who de repair are taken into account. signed and built America’s first pre cast concrete segmental box girder EVOLUTION OF bridge in 1973 — the John F. Kennedy PRECAST CONCRETE Memorial Causeway Bridge connect ing Corpus Christi and Padre Island, SEGMENTAL BRIDGES Texas — could have imagined that this The European Experience simple, unadomed structure would be Originating in Europe, this versatile the harbinger of some of the nation’s and economical bridge type emerged W. Denney Pate, RE. most beautiful and affordable bridges. shortly after World War II. With the Senior Vice President and Indeed, thirty years later, precast urgent need to reconstruct bombed-out Principal Bridge Engineer concrete segmental construction has FIGG Engineering Group bridges quickly and efficiently, and Tallahassee, Florida produced some of the most technolog with steel production capacity debili ically advanced, visually dramatic, tated by war efforts, European design and environmentally sensitive struc ers and builders turned to prestressed tures in North America as well as in concrete. 26 PCI JOURNAL ____________ The first precast concrete segmental bridge, the Luzancy Bridge across the Marne River in France, was erected in 1946. It was designed and built by Eu gene Freyssinet, the French engineer and pioneer whose technical investiga tions and ingenious advances during the first half of the 20th Century made prestressed concrete a viable construc tion material. While numerous precast, prestressed concrete bridges were built throughout Europe between 1946 and 1973, American bridge designers did not im mediately embrace this new technol ogy, in part because many conven tional bridge engineers of the time questioned the suitability of using pre cast concrete segments for major or long-span structures. However, with further advancements in technology, precast, prestressed concrete emerged as a strong competitor to conventional construction. Lee Roy Selmon Expressway A compelling example of the phe nomenal evolution of precast concrete segmental bridges since 1973 is presently under construction in Tampa, Florida — where the Pre stressed Concrete Institute (PCI) was founded in 1954. The three-lane re versible structure erected span-by- span within the median of the Lee Roy — Selmon Expressway, on single piers Fig. 1. Presently under construction over moving traffic, the Lee Roy Selmon only 6 ft (1.8 m) wide Expressway at the base, will in Tampa, Florida, supports six lanes of traffic on single piers only 6 ft more than double the toll highway’s (1 .8 m) wide, and demonstrates the extraordinary evolution of precast concrete capacity within the existing right-of- segmental bridges in the last thirty years. way while maintaining essential traffic flow during construction (see Fig. 1). Operating in the direction of peak de ing hours, all lanes are open while The bridge piers also present mand (westbound from the suburbs to workers apply epoxy between the seg sculpted shaping, with curved flares at downtown Tampa in the morning and ments and post-tension the tendons, the top and a 3 in. (76 mm) recess eastbound in the evening), the 5-mile without impeding traffic below. A along the vertical faces. With a soft (8 km) long structure will provide “six typical 140 ft (42.7 m) span requires color finish and accent lighting from lanes in 6 feet,” preserving most of the about three days to complete. below, the bridge will be a striking median for future use. Designed by Figg Bridge Engineers feature of the Tampa landscape when The 3032 prestressed segments [59 and built by PCL Civil Constructors, completed in 2006. ft (18 m) wide, about 70 tons (64 the sculpted curved forms of the super Part of a $350 million expansion tonnes)] are precisely cast at a nearby structure and piers embody the vision program that includes several miles of factory and delivered by truck during of the Tampa-Hillsborough Express park-like boulevards providing local off-peak hours. In the immediate area way Authority for an aesthetically access to and from the reversible ex of the worksite, the inside lanes of the unique bridge — truly, a landmark press lanes at each end, the segmental four-lane roadway are temporarily structure. The precast concrete box bridge contains approximately 1.6 closed while the segments are lifted girder has curved geometry in the million sq ft (148,640 ) m2 of deck. onto the self-launching, underslung webs, corners, and the underside of the According to the Expressway Author erection girder. During peak commut barrier. ity, the Lee Roy Selmon Expressway September-October 2004 27 bridge is being constructed for $65 per This rapid transit bridge is only one COASTAL ENVIRONMENTS ft 2), currently sq ($700/rn or about 30 example of several other significant Among the advantages touted by its percent less than other major bridges segmental bridge projects currently champions was the ease and economy in Florida. under construction. of maintenance for precast concrete bridges, particularly in coastal envi ronments. Bridge maintenance was one of the concerns of the Florida De partinent of Transportation (FDOT) engineers in the mid-1970s as they considered replacement options for the decaying bridges of the Overseas Highway, the transportation lifeline of the Florida Keys. Long Key Bridge A Tallahassee, Florida-based civil engineer with a penchant for innova tion, Eugene Figg, proposed precast concrete segmental bridges as the so lution. And further, he suggested that FDOT request federal funds to finance a demonstration project of precast concrete technology for bridges in coastal environments. When the Fed Fig. 2. With the first eral Highway Administration agreed “as cast” riding to his proposal, Figg designed and in surface in the spected the construction of the Long United States, the Key Bridge. Michael Construction Co. 2.3 mile (3.7 krn) completed the 12,040 ft (3670 m) Long Key Bridge in structure in 1980 — five months ahead the Florida Keys of schedule — at a cost of $15.3 mil was completed at a lion, at a remarkable cost of $32.66 cost of $32.66 per per sq ft ($352/m2). sq ft ($352/rn2) in 1980, confirming Erected using the span-by-span the economic method, the 103 spans, with typical feasibility of precast lengths of 118 ft (36 m), were deliv concrete segmental ered by barge, installed as a unit, technology. aligned, and then post-tensioned. The Fig. 3. The longest continuous precast segmental bridge in the world in 1982, the Seven Mile Bridge in the Florida Keys was the first use in North America of precast, match-cast box piers, assembled with vertical post- tensioning. 28 PCI JOURNAL post-tensioning tendons were external to the box girder web, which reduced material costs and construction time. The Long Key Bridge was the first “as cast” riding surface in the United States (see Fig. 2). Seven Mile Bridge Soon thereafter, Misener Marine Construction started the nearby Seven Mile Bridge. Spanning 35,867 ft (10,932 rn), it was the longest continu ous precast segmental bridge in the world in 1982. The precast segments for the piers and superstructure were manufactured in Tampa and barged 450 miles (724 km) to the erection site south of Marathon Key. An overhead gantry lifted each of the 268 spans [135 ft (41.2 m) typical length] into position as a unit. The su perstructure was erected on precast, match-cast box piers that were assem bled with vertical post-tensioning (see Fig. 3). These design innovations al lowed a 60 ft (18.3) tall pier to be con structed in one day and three 405 ft (123 m) spans to be erected per week. The $45 million Seven Mile Bridge was $7 million less than the alterna tive solution, and was completed six months ahead of schedule. The project won a PCI Design Award in 1982. Fig. 4. Completed in 1982, the Linn Cove Viaduct, part of North Carolina’s Blue Ridge Parkway, was the first concrete segmental bridge in America to be built in one directional cantilever from the top down to protect the fragile environment. Black iron ENGINEERING AND oxide in the concrete mix allows the bridge to blend into the natural mountain hues. AESTHETICS Eugene Figg’s designs were a deci As a consequence of the firm’s vi for years, resulting in a “missing link” sive demonstration of the con sion, its clients’ projects have earned in this scenic region (see Fig. 4). structability, efficiency and economy more than 200 awards, including three The first in America, a precast con of precast concrete segmental con of the five bridges ever honored with crete segmental bridge proved to be struction. Founded in 1978, the firm, the Presidential Award for Design Ex the solution, constructed from the top now known as the Figg Engineering cellence by the National Endowment down in unidirectional progressive Group (FIGG), has continued to pio for the Arts (Linn Cove Viaduct, the cantilever.